I noticed some of your Ball Markers, like the RBM and Mega Marker are quite large. Do the rules of golf specify what type and size of object are acceptable to use as ball marker on the putting green? Do the rules prohibit  the use of any particular objects as ball markers on the green?

The rules (Rule 20-1) only state that the marker should be (as opposed to must  be) marked using a “ball-marker, a small coin or other similar object. The USGA and R&A consider it “appropriate” for players to use a small, round, relatively flat object – whether this is a coin, or something specifically manufactured for use as a ball marker.  But the governing bodies do not require such an object be used. (That’s the difference between using “should” or “must” in the note to Rule 20-1 quoted above.)  Rule 20-1 offers several examples of unorthodox ways to mark a golf ball on the green, each of which are fine although they do not conform with the request of the Note to Rule 20-1:
⦁ -placing the toe of a club at the side of, or behind, the ball
⦁ -using a tee
⦁ -using a loose impediment
All of the above methods go against the “recommendation” in the Note to Rule 20-1; remember, you should use something small, round and relatively flat such as a coin or an object specifically manufactured as a ball marker. But the fact is, you could mark your ball with a cupcake if you wanted to. That would be very poor etiquette, and you shouldn’t do it – but there’d be no penalty. (Unless you’re playing with me, in which case I might eat your ball marker.)